This proposal addresses two observations: 1) five different isotypes of sPLA2 exist in human lung, three of which could cause surfactant dysfunction and 2) surfactant dysfunction occurs in acute asthma. Little is known about the pulmonary distribution or functions of these potentially toxic sPLA2S. The central hypothesis of the proposal is that the five isotypes of sPLA2 will have distinct cellular localization and enzymatic activities. The roles that these sPLA2s play in pathologic events are important and potentially remediable. The proposal will address the following aims: 1) Hypothesis: That the five distinct sPLA2s in human lung will have different cellular localizations within the lung. Plan: Use in situ hybridization to localize mRNA, and Group-specific anti-sPLA2 antibodies to localize sPLA2 proteins in lung and airway tissues and in isolated cells (eosinophils and macrophages) and cell lines (e.g., NHBE bronchial epithelial cells) and in lung and airway tissues of allergen-challenged asthmatics. 2) Hypothesis: That the five sPLA2 isotypes will have distinct abilities to hydrolyze phospholipids (PL) including surfactant. Plan: Using mixed micellar assays and monomolecular film techniques, determine enzyme kinetics and effect of surface charge and phospholipid head group packing on sPLA2 binding to and hydrolysis of specific phospholipid substrates and mixed substrates as occur in human surfactant. Determine in detail the changes in biophysical properties of PL (including surfactant) induced by sPLA2 hydrolysis. 3) Hypothesis: sPLA2-mediated surfactant dysfunction will be the result of multiple mechanisms including: generation of lysophospholipids and unsaturated fatty acids, conversion of large functional surfactant aggregates to small dysfunctional surfactant aggregates and selective depletion of phospholipids such as phosphatidylglycerol (PG) within the mixed surfactant micelles. Plan: Quantitate in vitro hydrolysis of specific PL species within surfactant and determine effects on surfactant function. Determine if reconstitution of specific PLs are more effective in restoring surfactant function. Conversely, determine concentrations of specific PLs and fatty acids that induce similar dysfunction. 4) Hypothesis: That allergen challenge in patients with asthma causes surfactant dysfunction and that this is due in part to hydrolysis of surfactant PL, with specific changes as will be defined in aims 1-3. Plan: Characterize the nature of surfactant damage dysfunction occurring in asthmatics after allergen challenge. Determine if surfactant damage correlates with indices of disease activity, local cells and mediators. Determine if alterations in surfactant composition and function in vivo match the effects of sPLA2s on surfactant composition and function in vitro. Identify if other factors (e.g., inflammation-related proteins) contribute to dysfunction.